Mobile communication architectures can be categorized as cellular networks and ad-hoc networks. In a cellular network, direct communication between mobile devices is usually not permitted. Traffic is generally routed via one or more core network elements even if the source and destination are close to each other. Contrary, in ad-hoc networks, mobile devices can communicate directly with each other without involving a (core) network infrastructure such as a centralized controller. This is referred to as device-to-device (D2D) or peer-to-peer (P2P) communication.
Enabling additional D2D communications in cellular networks was found to potentially become a promising concept. According to such concept, local D2D communication benefits from the centralized controlling of cellular system such as resource allocation and interference coordination. Also, the efficiency of a cellular system can be improved by exploiting channels of high quality for short-range D2D links.
Advantages of introducing D2D communication into a cellular system may, for example, include: longer battery life of mobile device's batteries due to reduced transmission power requirements, more efficient resource usage because of direct routing of D2D traffic, improved performance of content distribution applications by using inter-recipient transmissions, etc.
D2D communication as an underlay to the cellular networks has been proposed to be a key technology component for the International Mobile Telecommunications-Advanced (IMT-Advanced) networks. In this report, D2D communications using Long Term Evolution (LTE) standard technology for the enhancement of cellular system is referred to as LTE D2D.
Generally, the invention pertains to centralized wireless networking combined with an additional ability of D2D communication. Devices such as mobile devices can communicate via a centralized station, such as a centralized control unit or the like, at least partially routing the communication between two or more devices. The centralized control unit may be part of the core network infrastructure. Especially, the centralized station is usually aware of those devices which are in a communication range with the centralized station. The devices need not be mobile. They can also be stationary. They may be user equipments such as cellular phones, smart phones, laptop's, or the like. Although wireless communication is usually established via radio as a transmission resource, it may also be applied to ultrasonic, infrared light or the like as transmission resource. The transmission resource may be limited to a certain band or divided in certain bands, wherein a band defines a wavelength range or a frequency range, respectively.
Herein below, however, exemplary aspects of the invention will be described with reference to radio communication as wireless communication.
A certain application may provide for a D2D communication feature sharing the same band of a transmission resource with other communication applications such as Industrial, Scientific and Medical (ISM) appliances as e.g. WLAN, Bluetooth™, ZigBee™, or the like. ISM applications often do not require a license for operation which is why such bands may also be referred to as unlicensed bands or license exempt bands. In contrast hereto, communication via networks commonly require an agreement (for license) on which bands are to be used/reserved. This is why it may also be referred to as licensed bands. In many cases, the D2D communication as well as communication of ISM appliances can be locally limited. Therefore, interference may inter alia appear when the communication ranges of the D2D communication and the communication of ISM appliances spatially and temporally overlap. Such shared bands require specific conditions so that interferences between the communications can be avoided to some extent. For this purpose, it is known in the art to use certain handshaking procedures such as, e. g. in relation to WLAN, Carrier Sense Multiple Access/Collision Avoidance CSMA/CA in order to reduce interference.
Irrespective thereof, some communication interference may arise during different communications in a shared band although using CSMA/CA. The problem envisaged is supposed to be further detailed on the basis of a specific situation in which centralized wireless network-based communication is provided by LTE technology in combination with D2D communication in the same band as free local communication, which band can be an ISM band. The following discussion is not to be understood to limit the scope of the invention but to improve the ease of understanding only.
It is envisioned that LTE technology usage on shared bands can provide: 1) new markets to LTE technology based radio systems; 2) additional capacity to cellular system operation; 3) new applications and communication solutions using LTE modem technology such as wireless machine-to-machine (M2M) and D2D communications. Therefore, although most recent research works assume that LTE D2D should be operated on the licensed bands to guarantee a controlled interference environment, the benefits of using license exempt bands (also referred to as unlicensed bands), such as the 2.4 GHz (ISM) band, to perform LTE D2D communication have not been sufficiently taken into account.
In a D2D communication underlying cellular concept, such as LTE D2D, D2D communication can be established via three successive stages:
1) the gateway detects and earmarks any potential D2D traffic by checking source and destination IP addresses;
2) a D2D radio bearer for each D2D communicating pair is set up with the help of MME and eNB; and
3) the eNB allocates a resource for each D2D communicating pair.
The stage 3 of this concept can also be regarded as a D2D communication setup. In this concept, the D2D communications are using licensed resource of cellular system so that the eNB can directly allocate resource for the D2D pair.
In order to facilitate LTE D2D operating e. g. on ISM band, the main challenges are related to a co-existance of LTE D2D and the popular IEEE 802.11 standard related to WLAN in the same frequency band and geographical area.
Some studies tried to achieve a fair resource contention for both LTE D2D and e. g. WLAN, Bluetooth™, ZigBee™ by using for example CSMA/CA mechanism such as e. g. specified in IEEE 802.11 DCF. The basic idea is that, by the exchange of request to send/clear to send (RTS/CTS) messages, D2D devices can silence WLAN terminals within their signal coverage and thus use the resource on an ISM band without severe interference.
WLAN terminals being out of the signal coverage of D2D devices communicating are not aware of an ongoing D2D communication between those devices. In this case, if a centralized control unit such as a home evolved node_B (HeNB) wants to regulate the D2D communication between the D2D devices, the control signaling and/or D2D status report may be interfered by such nearby WLAN terminals.
The co-existence problem as outlined above between a LTE D2D and a WLAN system of the present example and based on a conventional resource contention scheme using CSMA/CA mechanism is shown in FIG. 1.
FIG. 1 schematically depicts exemplary a situation of a LTE D2D communication contending with a WLAN operation. As a centralized control unit, a HeNB triggers the D2D communication between two user equipments UE1 and UE2. The HeNB, the user equipments UE1 and UE2 are assumed to be in an overlapping area of two communication ranges 70, 72 of the user equipments UE1 and UE2 as well. In this scenario, the user equipment UE1 is to transmit data to the user equipment UE2. Therefore, user equipment UE1 starts establishing D2D communication by broadcasting a certain request signal, namely, a RTS (request to send) signal. The user equipment UE2 receives this RTS signal and responds by broadcasting a CTS (clear to send) signal. The user equipment UE1 receives the CTS signal and starts to transmit the data.
FIG. 1 shows a certain area designated as RTS-coverage. This area is the communication range 70 of the user equipment UE1. Moreover, FIG. 1 shows a further area designated as CTS-coverage. This area is the communication range 72 of the user equipment UE2. As can be seen from FIG. 1, communication ranges 70, 72 overlap. In the overlapping portion of the communication ranges 70, 72, the user equipments UE1 and UE2 are located.
Additionally, WLAN terminals W1 through W4 are shown. The WLAN terminals W1 and W2 are outside of any of the communication ranges 70, 72. However, the WLAN terminals W1 and the W2 are located close to the HeNB. The WLAN terminal W3 is located in the communication range 70 of the user equipment UE1. The WLAN terminal W4 is located in the communication range of the user equipment UE2. The operation can be as follows:
As a source D2D device, the user equipment UE1, willing to transmit a data packet to the user equipment UE2 as a destination D2D device, first senses the medium. In this scenario, the medium is instantly the ISM radio band 2.4 GHz which is often used for WLAN services.
The term “medium” corresponds to a first resource as will become apparent later. If the medium is busy then it defers. If the medium is free for a specified time such as a Distributed Inter Frame Space (DIFS) according to the IEEE 802.11 standard, then the user equipment UE1 is allowed to transmit a short control packet called Request to Send (RTS) signal which includes a source address, a destination address, and a duration of the following D2D communication.
In response to receipt of the RTS signal, the user equipment UE2 responds, if the medium is free, with a response control packet called Clear to Send (CTS) signal which includes the same duration information as the RTS signal.
All the WLAN stations receiving either the RTS signal and/or the CTS signal such as e.g. the WLAN stations W3 and W4 in FIG. 1, keep silent for the given duration in the RTS signal or the CTS signal. By this means, the medium is reserved for the D2D communication between the user equipment UE1 and the user equipment UE2 without inter-system interference.
This mechanism can protect the transmitter area (RTS coverage indicated by reference character 70 in FIG. 1) and the receiver area (CTS coverage indicated by reference character 72 in FIG. 1) from collisions during D2D communication duration. However, it can not protect the signaling interactions between the HeNB and the D2D communicating user equipment pair UE1, UE2.
WLAN terminals being close to the HeNB but out of the signal coverage of the RTS signal and the CTS signal such as the WLAN terminals W1 and W2 in FIG. 1 are not aware of the ongoing D2D communication. So, interference can appear by the WLAN terminals W1 and/or W2 communicating although D2D communication between the user equipment UE1 and the user equipment UE2 is established.
It should be noted that LTE D2D communication are always performed under the control of the HeNB, for the purposes of resource scheduling, session setup, security, QoS, charging, policy enforcement and etc. The signaling interactions between a HeNB and a D2D communicating pair, such as a D2D status report and resource/power control packet, should be protected from inter-system interference. The existing scenarios can not overcome this problem.
Hence, it is an object of the invention to further improve such scenarios.